<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=800">
<style>
html { font-size: 16px; }
body { width: 800px; margin: 0; overflow-y: hidden; }
</style>
</head>
<body>
<div style="font-size: 2.5rem">
    <div style="width: 600px">
        This text should be autosized to 40px computed font-size as it is a part of the same cluster as the parent div.<br>
        Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
    </div>
    <div style="width: 320px; font-size: 1rem">
        This text is not autosized since it's too narrow and is considered to be a separate autosizing cluster.
    </div>
</div>
</body>
</html>
